1. Field
The described technology relates generally to a micro-truss structure and the use of the micro-truss structure in a material or apparatus for controlling the environmental state of a working surface (e.g., a micro-truss perspiration control layer for controlling airflow to a human body).
2. Description of Related Art
A number of approaches currently exist on the market to improve air flow through structures or materials that are expected to have long-duration contact with some portion of a human or animal body, usually constituted from some kind of foam padding. Most often this padding is closed-cell foam. The most relevant of these approaches generally rely on manufacturing air flow pathways into the closed cell foam. Examples include shoe insoles with holes, “egg crate” foam padding, honeycomb materials, formed solid materials or open-cell foams, and thin stretched web-like or loose-weave fabrics.
However, without significantly compromising their stiffness and strength, honeycomb materials generally only allow airflow in a single direction. Commercial examples used in seating and bedding applications include Supracor® fusion bonded honeycomb. However, such “vented” honeycombs generally have a much greater overall weight than non-vented honeycombs in order to make up for the degradation of its mechanical properties.
Solid materials with defined airflow paths have also been used, but are generally uncomfortable. Although airflow is increased in the region of the airflow passages, areas where solid material contacts skin, generally become sweaty and uncomfortable.
In addition, subjecting the above-discussed materials or structures to compressive forces (e.g., when a person is sitting on the material) generally causes densification of the materials or structures (e.g., reduction in the open volume of the material), which can close or reduce the size of airflow paths (or pathways), thereby reducing total airflow through the material.
Thin, stretched web-like, or loose weave fabrics are designed to provide support through tension of the fabric and to provide airflow due to the loose weave. Tension is generally provided by a hard frame around the perimeter of the web or weave. Commercial examples include the Herman Miller® Aeron® Chair, and the Saddleco™ Flow™ bike seat. These approaches do enable increased airflow, but have the disadvantage of being vulnerable to punctures and tears, limiting the overall usefulness in dynamic applications (e.g. sports).
An ordered three-dimensional (3D) microstructure is an ordered 3D structure at the micrometer scale. Currently, polymer cellular materials that are mass produced are created through various foaming processes, which yield random (not ordered) 3D microstructures. Techniques do exist to create polymer materials with ordered 3D microstructures, such as stereolithography techniques; however, these techniques rely on a bottom-up, layer-by-layer approach which prohibits scalability.
A stereolithography technique is a technique that builds a 3D structure in a layer-by-layer process. This process usually involves a platform (substrate) that is lowered into a photo-monomer (photopolymer) bath in discrete steps. At each step, a laser is scanned over the area of the photo-monomer that is to be cured (polymerized) for that particular layer. Once the layer is cured, the platform is lowered by a specific amount (determined by the processing parameters and desired feature/surface resolution) and the process is repeated until the full 3D structure is created. One example of such a stereolithography technique is disclosed in Hull et al., “Apparatus For Production Of Three-Dimensional Objects By Stereolithography,” U.S. Pat. No. 4,575,330, filed Aug. 8, 1984, which is incorporated by reference herein in its entirety.
Modifications to the above described stereolithography technique have been developed to improve the resolution with laser optics and special resin formulations, as well as modifications to decrease the fabrication time of the 3D structure by using a dynamic pattern generator to cure an entire layer at once. One example of such a modification is disclosed in Bertsch et al., “Microstereolithography: A Review,” Materials Research Society Symposium Proceedings, Vol. 758, 2003, which is incorporated by reference herein in its entirety. A fairly recent advancement to the standard stereolithography technique includes a two-photon polymerization process as disclosed in Sun et al., “Two-Photon Polymerization And 3D Lithographic Microfabrication,” APS, Vol. 170, 2004, which is incorporated by reference herein in its entirety. However, this advanced process still relies on a complicated and time consuming layer-by-layer approach.
Previous work has also been done on creating polymer optical waveguides. A polymer optical waveguide can be formed in certain photopolymers that undergo a refractive index change during the polymerization process. If a monomer that is photo-sensitive is exposed to light (typically UV) under the right conditions, the initial area of polymerization, such as a small circular area, will “trap” the light and guide it to the tip of the polymerized region due to this index of refraction change, further advancing that polymerized region. This process will continue, leading to the formation of a waveguide structure with substantially the same cross-sectional dimensions along its entire length. The existing techniques to create polymer optical waveguides have allowed only one or a few waveguides to be formed and these techniques have not been used to create a self-supporting three-dimensional structure by patterning polymer optical waveguides.
Three-dimensional ordered polymer cellular structures have also been created using optical interference pattern techniques, also called holographic lithography; however, structures made using these techniques have an ordered structure at the nanometer scale and the structures are limited to the possible interference patterns, as described in Campbell et al., “Fabrication Of Photonic Crystals For The Visible Spectrum By Holographic Lithography,” NATURE, Vol. 404, Mar. 2, 2000, which is incorporated by reference herein in its entirety.
The use of metallic lattice (truss) materials is discussed in U.S. Pat. No. 7,382,959 (“Optically oriented three-dimensional polymer microstructures”) and U.S. patent application Ser. No. 11/801,908 filed on May 10, 2007; Ser. No. 12/008,479 filed on Jan. 11, 2008; Ser. No. 12/074,727 filed on Mar. 5, 2008; Ser. No. 12/075,033 filed on Mar. 6, 2008; Ser. No. 12/455,449 filed on Jun. 1, 2009; Ser. No. 12/928,947 filed on Dec. 22, 2010; and Ser. No. 13/437,853 filed on Apr. 2, 2012 which are incorporated by reference herein in their entirety. Various micro-truss structures and methods of manufacturing micro-truss structures are described, for example, in U.S. patent application Ser. No. 12/455,449, which discloses a method of fabricating micro-truss structures having a fixed area, U.S. patent application Ser. No. 12/835,276, which discloses a method of continuously fabricating micro-truss structures according to a continuous process (e.g., a strip of arbitrary length), U.S. patent application Ser. No. 12/928,947, which discloses a compressible fluid filled micro-truss for energy absorption, and U.S. patent application Ser. No. 12/317,210, filed on Dec. 18, 2008, which discloses a functionally graded three-dimensional ordered open cellular microstructure and a method of making the same, each of which is incorporated by reference herein in its entirety.